The present technology relates to fire protection systems, such as sprinkler systems.
A fire protection system, also known as a fire suppression or fire sprinkler system, is an active fire protection measure that includes a water supply to provide adequate pressure and water flow to a water distribution piping system, where the water is discharged via sprinklers or nozzles. Fire protection systems are often an extension of existing water distribution systems, such as a municipal water system or water well or water storage tank. The deterioration of piping, sprinkler heads, and hydraulics (the ability of the system to deliver water to design specifications) in fire protection systems can be attributed to the quality of the water being supplied from the water distribution source and corrosion of metallic components including ferrous metals and cuprous metal components within the system.
Deterioration and corrosion of fire protection systems may involve several factors. First, oxidative attack of the metal can produce corrosion deposits, or tubercles, that may partially block a water pipe thereby reducing the hydraulic capacity, requiring higher operating pressures and reducing fire protection. Or, in some cases, tubercles may fully block a water pipe or sprinkler head. Second, depletion of biocide in the water (originally applied by the municipal water supplier or water well or water storage tank) due to the presence of tuberculation, organic matter, and microbiological organisms associated therewith may result in microbiological growth. And third, leaks can result from general corrosion and/or microbiologically influenced corrosion, such as oxidation by trapped air, and the use of higher operating pressures. These factors may operate together to severely compromise the performance of the fire protection system.
Microbiological influenced or induced corrosion (MIC) can result when waterborne or airborne microbiological organisms, such as bacteria, molds, and fungi, are brought into the piping network of the protection system with untreated water and feed on nutrients within the piping system. These organisms establish colonies in the stagnant water within the system which can occur even in dry pipe sprinkler networks where significant amounts of residual water may be present in the piping network after a test or the activation of the system. Over time, the biological activities of these organisms cause significant problems within the piping network. Both ferrous metal and cuprous metal pipes may suffer pitting corrosion leading to pin-hole leaks. Iron oxidizing bacteria form tubercles, which can grow to occlude the pipes. Tubercles may also break free from the pipe wall and lodge in sprinkler heads, thereby blocking the flow of water from the head either partially or entirely. Even stainless steel is not immune to the adverse effects of MIC, as certain sulfate-reducing bacteria are known to be responsible for rapid pitting and through-wall penetration of stainless steel pipes.
Corrosion within a fire protection system can also occur or can increase following operation or testing of the system. For example, when the piping of a dry pipe or preaction sprinkler system is drained after testing, residual water collects in piping low spots and moisture is also retained in the atmosphere within the piping. This moisture, coupled with the oxygen available in the compressed air in the piping, increases the pipe internal wall corrosion rate, possibly leading to leaks. Oxygen and microbiological organisms also contribute to the internal pipe wall corrosion rate in wet pipe systems in which the piping is maintained full of stagnant water providing a medium in which the organisms can grow.
In addition to MIC, other forms of corrosion are also of concern. For example, the presence of water and oxygen within the piping network can lead to oxidative corrosion of ferrous materials. Such corrosion can cause leaks as well as foul the network and sprinkler heads with iron oxide particles (e.g., rust particles) in the form of hematite (Fe2O3) or magnetite (Fe3O4), deteriorating the system hydraulics. Presence of water in the piping network having a high mineral content can also cause mineral scale deposition, as various dissolved minerals, such as calcium, magnesium, and zinc, react with the water and the pipes to form mineral deposits on the inside walls. In the presence of dissolved oxygen, these deposits can act to accelerate corrosion of the pipe just beneath the deposits. These deposits can inhibit water flow or can break free and clog sprinkler heads, preventing proper discharge of water in the event of a fire.
A need, therefore, exists in water-based fire protection systems for methods that reduce corrosion of the fire sprinkler system and deterioration of the fire protection system's performance.